This invention relates to a friction-wear aluminum part and an associated method. More particularly, the invention relates to vehicle parts, such as brake rotors, brake drums, flywheels and the like which have at least a portion of their wear surface coated with a friction-wear coating. On a preferred basis, the brake parts and flywheels themselves are also made of aluminum alloys.
"Light-weighting" of vehicles, such as automobiles, is a process of substituting lighter materials, such as aluminum, for heavier materials, such as steel. Some of the obvious advantages of light-weighting are that fuel economy is improved and that less powerful engines are needed to propel such vehicles.
There are several cast iron or steel parts in a vehicle, including brake rotors, brake drums and flywheels. One light-weighting solution, therefore, would be to substitute a light-weight aluminum brake rotor for its heavier cast iron counterpart. However, attempts to make this substitution have not met with success because aluminum brake rotors tend to scuff and score more easily, thus making it less feasible to replace cast iron versions with aluminum equivalents.
Solutions to the latter problem have been proposed. One such proposal in U.S. Pat. No. 3,069,209 discloses a cast iron liner in a light-weight aluminum part, such as a brake drum. Still another proposed solution, in British Patent Application No. 2,268,511 A, sprays a simulated cast iron coating on a substrate before the coating is surface heat treated.
In order to be effective, any friction-wear coating must have good resistance to wear, good high temperature stability and thermal conductivity, good adhesion to aluminum, good machinability and finally solution potentials and coefficients of thermal expansion close to that of the aluminum substrate onto which the coating will be applied. The casting itself should be inexpensive and the coating cost effective to apply. Coatings with good high temperature stability are needed to resist melting and subsequent brake fade. Good thermal conductivity is also necessary to transfer frictional heat from the outer coating to the aluminum drum or rotor substrate. This coating must also have good adhesion to aluminum and a coefficient of thermal expansion so close to that of aluminum as to prevent bond failure during braking due to thermal shock. The coating solution potential must also be close to that of the aluminum substrate in order to prevent galvanic corrosion there between.
Despite the existence of prior art friction-wear parts and coatings, there still remains a need for automotive brake parts, especially aluminum versions thereof, having a friction-wear coating applied thereto which meet or exceed the above requirements, while at the same time being inexpensive to manufacture and coat.